The main components of a drive train of a motor vehicle are a drive assembly and a transmission. The transmission converts torques and speeds, and thus transforms the traction force produced by the drive assembly. The present invention concerns a method for operating a drive train that comprises at least a transmission and, as the drive assembly, a hybrid drive with an internal combustion engine and an electric motor.
In a drive train with so-termed parallel hybrid drive, a clutch is connected between the internal combustion engine and the electric motor of the hybrid drive, by means of which the internal combustion engine of the hybrid drive can be disengaged from a drive output of the drive train. When such a drive train with a parallel hybrid drive is started, the internal combustion engine is typically switched off and the clutch connected between the internal combustion engine and the electric motor is disengaged.
Then, when the switched-off internal combustion engine is to be started, this can be done by at least partially engaging the clutch connected between the internal combustion engine and the electric motor so that the internal combustion engine is entrained into motion by the electric motor, and to carry out this entrainment optimally the point in time must be known, from which the internal combustion engine has been started and is actively producing a torque. Until now that time point has been determined in a motor control unit from the number of ignition sparks of the internal combustion engine. However, that is relatively inaccurate.